From Robert Silverberg’s, “Earthmen and Strangers” anthology, 1966: Earthly life has developed many methods of reproducing itself. The amoeba is content to split in half; the hydra produces a bud that develops into a new hydra; the small crustacean known as daphnia lays eggs that do not need to be fertilized in order to bring forth young daphnias. Most animals, though, rely on two sexes, female...